1. Field of the Invention
The present invention relates to a turbo compressor and a refrigerator. More specifically, the present invention relates to a turbo compressor capable of compressing a fluid by a plurality of impellers and a refrigerator including the turbo compressor.
Priority is claimed on Japanese Patent Application No. 2009-170193, filed Jul. 21, 2009, the content of which is incorporated herein by reference.
2. Description of Related Art
There is known a turbo refrigerator or the like including a turbo compressor which compresses and discharges the refrigerant by means of a compressing means equipped with an impeller or the like as a refrigerator for cooling or refrigerating a material to be cooled such as water.
In the compressor, if the compression ratio increases, the discharging temperature of the compressor rises and the volumetric efficiency declines. Thus, in the turbo compressor included in the turbo refrigerator or the like as described above, the compression of the refrigerant is often performed so as to be divided into a plurality of stages.
In such a turbo compressor, the lubricant oil is supplied to sliding parts such as a bearing from an oil tank. Furthermore, in order to release the refrigerant gas, which is generated in the oil tank when the compressor starts, to the inlet side of the compressor, a pressure equalization pipe for making the oil tank and the compressor communicate with each other is disposed (for example, see Japanese Patent No. 3489631).
The turbo compressor essentially continues to operate over a long time at a constant rotation speed. However, for the purpose of energy saving, the operation ON/OFF is frequently performed. At this time, in the case where only the pressure equalization pipe is disposed, when the compressor is stopped, the refrigerant flows backward from a condenser into the compressor inlet, so that the pressure of the compressor inlet increases, whereby the refrigerant flows backward from the pressure equalization pipe into the oil tank side. There is a problem that the refrigerant flows backward to the oil tank and leaks from a labyrinth seal into a compressor flow path or a motor, and, at this time, the lubricant oil, which is being refueled to the bearing near the labyrinth, is also taken out as oil leakage, whereby the amount of oil in the oil tank is reduced.